1. Technical Field
The present invention relates to an air conditioner having an outdoor unit and a plurality of indoor units, in which the plurality of indoor units can perform a cooling operation or a heating operation at the same time or the heating operation and the cooling operation can be performed in a mixed manner.
2. Background Art
In general, an air conditioner of a fluid pipe and a gas pipe connection type (hereinafter referred to as a “double pipeline type”) is known in which an outdoor unit and a plurality of indoor units are connected through two inter-unit pipelines made up of a fluid pipe and a gas pipe and the plurality of indoor units are made to perform the cooling operation or the heating operation. Also, recently, an air conditioner of a low-pressure gas pipe, a high-pressure gas pipe and a fluid pipe connection type (hereinafter referred to as a “triple pipeline type”) is proposed, in which the outdoor unit and the plurality of indoor units are connected through three inter-unit pipelines made up of a low-pressure gas pipe, a high-pressure gas pipe and a fluid pipe and the plurality of indoor units are made to perform the cooling operation or the heating operation at the same time or the cooling operation and the heating operation are performed in a mixed manner (See JP-B-2804527, for example).
In this type of triple-pipeline type air conditioner, if the plurality of indoor units are made to perform the cooling operation and the heating operation in a mixed manner, the three inter-unit pipelines are all used for the operations but if only the cooling operation or the heating operation is performed, two (the fluid pipe and the low-pressure gas pipe in the cooling operation and the fluid pipe and the high-pressure gas pipe for the heating operation) in the three inter-unit pipelines are used.
Here, in the cooling operation, since a low-pressure gas refrigerant evaporated in an indoor heat exchanger of the indoor unit fully flows through the low-pressure gas pipe and is sucked into a compressor of the outdoor unit, a pressure loss can easily occur due to channel resistance in the low-pressure gas pipe. If the pressure loss occurs, a sucking pressure of the compressor is lowered and a specific volume becomes large, and the capacity of the compressor is lowered, and thus, the cooling capacity of the air conditioner is deteriorated, which is a problem. In the meantime, if a pipe diameter of the low-pressure gas pipe is changed and increased, the pressure loss is reduced, and the drop in the sucking pressure of the compressor is suppressed, but a great cost is required.
On the other hand, in the above-mentioned prior-art triple-pipeline type air conditioner, since the outdoor unit is connected to the three inter-unit pipelines, the outdoor unit has more complicated configuration of devices connected by pipelines or routing of the pipelines as compared with the double-pipeline type outdoor unit, which tends to increase the size of the device configuration. Also, since the three inter-unit pipelines need to be provided, a piping cost is high and a piping work becomes complicated, which is a problem.